Air conditioning system



July 1942- A. R. STEVENSON, JR 2,289,082

I AIRCONDITIONING SYSTEM Filed May 27, 1941 2 Sheets-Sheet l Pg a Inventor: Alexander R. Stevenson JTT,

by W 6. JMMAM His Attorney.

y v A. R. STEVENSON, JR' 2,289,082

AIR CONDITIONING SYSTEM I Filed May 27, 1941 2 Sheets-Sheet 2 v Inventor: Alexander R. Stevenson Jr;

7v 6? AM /M His A torney.

. v Patented July AIR CONDITIONING SYSTEM Alexander R. Stevenson, Jr., Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application May 27, istnsei-iai No. 395,411

. 16 Claims.

My invention relates to air conditioning apparatus and particularly to electric motor driven refrigerating apparatus for cooling and dehumidifying the air within an enclosure.

Air conditioning systems which dehumidi'fy air by cooling frequently are required to operate un-,, 'der atmospheric conditions such that the cooling necessary to reduce the relative humidity of the air to a desired value'reduces the dry bulb temperature to a value too low for comfort. Under these conditions it'is necessary to provide for reheating of the dehumidified air before it is discharged into the room or enclosure being conditioned. The conditions requiring reheating are met most frequently during mild weather, that is during the cooling season when the dry bulb temperature of the outdoor air is of the order of 85 F. or lower. Within this range of temperature, little'sensible heat need be removed from the air, the amount depending primarily upon the heat load within the enclosure itself; and the full capacity of the refrigerating machine is, therefore, not required. Refrigerating machines for operation under theseconditions are sometimes provided with compressors driven by variable speed electric motors or other prime movers so that the speed may be reduced as the required capacity becomes lower. fective compressor capacity is desirable in order to prevent frequent starting and stopping of the driving motor which would be necessary if the compressor operated at full capacity whenever there was a demand for cooling.

It is an object of my invention to provide an air conditioning system including an electric motor driven compression type refrigerating machine and an improved arrangement for providing reheating of dehumidified air.

Another object of my invention is to provide an air conditioning system including a compression type refrigerating machine driven by an electric motor and an improved arrangement for making available heat for reheating dehumidified air under conditions of operation normally requiring reheating.

Further objects and advantages of my invention will become apparent as the following de- The air conditioning system shown in the draw-- ings comprises a conditioning casing or duct to which air from the room to be conditioned and fresh air may be admitted and circulated over A reduction of the ef- I a cooling coil and thence delivered to thereon The cooling coil is supplied with refrigerant or cooling fluid by a suitable refrigerating machine of the compression type driven by an electric motor. The motor is of the variable speed type utilizing a resistor or resistors in one of its circuits for effecting a reduction of speed. The

speed of the motor and hence the capacity of the refrigerating machine may be controlled-in accordance with. the temperature in the enclosure 50 that the speed' of the machine may be reduced as the sensible heat load is reduced. Under atmospheric conditions required dehumidification of the air supplied to the enclosure, the heat dissipated in the resistors of the motor speed control is madeavailable for reheating of the dehumidifled -air. .The controlv and the degree of reheating is eifected in accordance with changes in conditions .of the outdoor air. The

heat for reheating the air in the enclosure has been illustrated as supplied 'to air, circulated through a separate duct although any suitable scription proceeds, and the features of novelty i which characterize my invention will be .pointed out with particularity in theclaims annexed to and forming a part of this specification.

Foga better understanding of my invention reference may be had to the accompanying drawings, in which Fig. 1 shows diagrammatically an air conditioning system, embodyinl y invention;

arrangement for applying heat to the dehumidifled air in accordance with good air conditioning practice may be employed. In the illustrated arrangement the reheating'duct is separate from the main conditioning or cooling duct and may be employed for delivering heated air to the room or for discharging the heat generated in the resistors to the outdoors in the event reheating is not required. When there is a reduction in the speed of the compressor motor, heat is available in the speed control resistors and may be employed for reheating. Furthermore, the speed of the motor is controlled in accordance with the outdoor conditions, and, during normal operation of the system, heat is always available for reheating under those conditions of operation which require reheating.

The term condition" of air as employed in this specification and in the appended claims designates a condition of the air, which may be indicated on a psychrometric chart; among these conditions are wet bulb temperature, dry bulb temperature, relative humidity and moisture conten Referring now to the drawings, I have shown a portion of a building comprising outside walls i and i I and a partition wall I2 defining a room l3 which is to be conditioned and a machinery or service room l4. Within the service room 14 is arranged a duct or casing i 5 connected to receive room air through an inlet l6 and fresh air through an inlet 11 passing through the wall H to the outdoors. Air is circulated through the casing l5 by operation of a fan It driven by a motor I 9 and is delivered to the room through an outlet duct 20. In order to cool and dehumidify the air in the room, I provide a refrigerating machine including a compressor 2| driven by a three-phase alternating current motor 22 and arranged to supply compressed refrigerant to a condenser 23 and to withdraw vaporized refrigerant from an evaporator 24 arranged in the duct 15. During the operation of the compressor 2|, the compressed refrigerant is delivered to the condenser 23 where it is cooled and liquefied and flows to a liquid receiver 25. Liquid refrigerant from the receiver 25 flows through a liquid line 26 and thence to the evaporator 24 under control of a thermostatic expansion valve this heat, I- provide a duct 46 surrounding the resistors and a fan 41 driven by a-motor 68 for circulating air through the duct and over the .-'resistors. The motor 48 is connected to the sup- 21 having its thermal bulb or control element the drawings.

The operation of the refrigerating machine is controlled by energizing the motor 22 in accordance with the temperature of the air in the room I3 as determined by a thermostat 3i. Thermostat 3! comprises a movable contact 32 actuated by a coiled bimetallic element 33. Whenever the contact 32 moves to the right and engages a stationary contact 34, a solenoid switch is energized to connect the motor 22 across a threephase supply line 36, the solenoid of the switch 35 being connected across one phase of the supply line when the contacts 32 and 34 are engaged. The switch 35 also connects the motor l8 across the supply line 33 to operate the fan I8.

The motor 22 is a wound-rotor induction motor and is provided with a plurality of sets of resistors 31, 33 and 39 which may be connected in series with the windings of the rotor to vary the resistance of the windings and thereby vary the speed of the motor. Each of the sets of resistors 31, 38 and 39 comprises three resistors, one for each phase of the winding. The thermostat 3| is provided with three additional stationary contacts 40, 4| and 42 and when the contact 32 engages these contacts in order, it actuates short circuiting switches 43, 44 and 45 respectively. These switches short out the sets of resistors 31, 38 and 33 respectively, the closing of the switch 45 shorting all the resistors and ply line 35 by operation of the switch 35 and operates concurrently with the motors i9 and 22. Air to be circulated over the resistors may be taken in from outdoors through an inlet duct 49 and after being. heated by the resistors may be discharged outside the building through a discharge outlet 50,.

During some portions of the cooling season, particularly during mild weather when the dry bulb temperature is relatively low, the thermostat 3i may be satisfied by the reduction of the dry bulb temperature in the room but the relative humidity of the air may still be above the desired value so that it is desirable to continue the operation of the refrigerating machine to remove moisture from the air in the room. In order to accomplish this I provide a humidostat 56 which upon closing its contacts connects a I coil 52 of a solenoid switch 53 across one phase of the supply lines 36, thereby actuating the switch 53 and connecting the solenoid of the switch 35 across one phase of the supply lines 35 through the lower contacts of the switch 53. The

providing minimum resistance of the rotor windthe demand for cooling.

- At reduced speeds oi themotorv 22.when one or more of the sets of resistors 31, 33 and 33 are in'the circuit of the motor rotor, heat is generated in the resistors; and, in order to remove upper contacts of the switch 53 prepare a circuit for an outdoor thermostat 54 having a movabie contact 55 and three stationary contacts 55, El and 55 connected respectively to the solenoids of the switches 43, 44 and 45 on the same side as the contacts 40, 4| and 42, respectively, of the thermostat 3|. The movable contact 55 of the thermostat 54 engages the stationary contacts 58, 51 and 58 in order as the temperature rises, and the speed of the motor 22 is thereby determined in the same manner as by operation of the thermostat 3!. The humidostat 5! is therefore arranged to control the operation of the refrigcrating machine to dehumidir'y 1 air passing through the casing I 5, the speedloi the compressor 2| being determined in accordance with the dry bulb temperature of the outdoor air. The lowerthe temperature of the outdoor air, the lower is the speed of the compressor.

Should the operation of the refrigerating machine upon a call-for dehumidification, as deter mined by the humidostat 5i, reduce the dry bulb temperature of the air in the room I3 below a .predetermined minimum desirable limit, asnapacting thermostat 59 will close its contacts and operate a relay 60 to connect two solenoids 3i and 52 across one of the phases of the supply lines 38. The solenoids BI and 62 are arranged to actuate two dampers 63 and 64, respectively, so that the damper 63 closes the inlet duct 59 and the damper 54 closes the discharge duct 50. When the dampers 33 and 34 are in their actuated positions, the fan 41 circulates air from the is increased and short cycling is prevented. At

the same time the heat which is made available by the reduction of the speed of the motor may be utilized for reheating the air in the enclosure. This feature further insures a longer period of provided. These switches are energized simultav neously with the switches 43, 44 and 45, either by operation of the refrigerating machine and thus helps to reduce objectionable short cycling.

During the operation of the air conditioning system just described, the refrigerating machine normally-would be controlled in accordance with room temperature by operation of the thermostat 3| and as long as the thermostat 3| is not satisfied the refrigerating machine will be maintained in operation by the thermostat. When the thermostat is. satisfied and the relative humidity of the air in the enclosure remains above the desired maximum value, the humidostat 5| will close its contacts to continue the operation of the refrigerating machine, the speed of the operation under this condition depending upon the position of the outdoor thermostat 54. Should the continued operation of the com: pressor reduce the dry bulb temperature of the room below a desired minimum, the thermostat 7 59 will actuate the dampers 62 and 63 to utilize the heat generated in the resistors 31, 38 and 39 by reheating the air in the room. The requirements for reheating normally occur during mild weather conditions and the speed of the motor during such conditions and under operation of the humidostat is determinedby the outdoor-thermostat 54.

While I have shown the air heated by the resistors 31, 38 and 39 utilized for reheating by admitting the heated air directly to the room, it is obvious that any other arrangement for applying the reheat in accordance with good air conditioning practice may be employed. In some installations it might be advisable to join the ducts and 66 so that the heated and cooled air streams would be mixed before admission to the room, this arrangement being shown in Fig. 2. In other cases it might be desirable to locate the resistors 31, 38 and 39 in the main air conditioner, for example, in the casing l5 between the evaporator 24 and the fan l8. Furthermore, it might be desirable to provide two groups of the resistors 31, 38 and 39, one in the heat dissipating duct 46 for discharging the heat outdoors and the other in the casing l5 for heating the air after it passes over the evaporator. These latter two arrangements are shown in Fig. 3 in operation of the indoor thermostat 3| or the outdoor thermostat 54. It will, therefore, be, ap-' parent that the speed of the motor selected by either of the thermostats will be the same regardless of which of the groups of resistors is selected by the switch 81 and the switch 61 performs the same functio in Fig. 1 and thus makes possible the reheating of the air circulated in the duct l5 by heat generated in the speed controlling resistors. Since the thermostat 59 operates only after the thermostat 3i has been satisfied, it is readily apparent that the resistors 31a, 88a and 39a are connected in the rotor circuit only in accordance with the operation of the outdoor thermostat 54. The resistors 31, 38 and 89 normally are controlled only in response'to the indoor thermostat 3|. "However, it will be obvious that the outdoor thermostat 54 may, under certain conditions, take control after there has been a demand by the humidostat 5| for reduction of humidity and before the temperature in the room l3 has been reduced sufficiently to cause operation of the thermostat From the foregoing it is readily apparent that I have provided a simple and effective arrangement for making possible the reheating of dehumified air under conditions which normally require reheating, and that this arrangement provides an economical and eflicient system permitting the compressor to operate for a longer period at reduced capacity and minimizing short cycling of the refrigerating machine.

, While I have shown a particular embodiment of my invention in connection with a system for controlling the dry and wet bulb temperatures of the air within a room, other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention to be limited to the particular construction shown and described and I intend in the appended claims to cover all modifications within the spirit and scope of my invention What'I claim as new and desire to secure by Letters Patent of the United States is:

which the same numerals have been employed to indicate parts of the system which correspond to those in Fi 1.

The air conditioning system shown in Fig. 3 differs from that shown in Fig. 1 in that a second set of motor speed control resistors 31a, 38a and 39a is provided and is arranged in the duct l5 between the evaporator 24 and the fan I8 so that air cooled by the evaporator may be reheated by passing over the second set of resistors. The ducts and 86 are not employed in Fig. 3, and instead of controlling the dampers 62 and 83 at low temperature, the room thermostat 59 operates a change-over switch 61 whereby either the group of resistors 31, 38 and 39 or the group of resistors 31a, 38a and 39a may be connected in the rotor circuit of the motor. The switch 61 is biased to the leftby compression spring 68 and normally connectstheresistors 31, 38 and 39 to the rotor windings ofthe motor. However, when the thermostat 59 operates on low temperature it energizes a .coil 69 and moves the switch 81 to the left, thereby connecting the resistors 31a, 38a

" and 39a to the rotorwindings. In order to select 1. Apparatus for conditioning the air within an enclosure including a refrigerating machine comprising a compressor and a condenser and an evaporator for cooling the air in the enclosure, an electric motor fordriving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, and means dependent upon a predetermined condition of the air in the enclosure for actuating said control apparatus to operate said motor at a reduced speed. and for supplying to the air'in the enclosure heat generated in said resistor.

2. Apparatus for conditioning the air within an enclosure including a refrigerating machine com prising a compressor and a condenser and an evaporator, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means arranged to utilize said evaporator for cooling and dehumidifying air .to be discharged into said enclosure, means dependent upon a high relative humidity of the air in the enclosure for actuating said control apparatus to operatcsaid motor at as dampers 82 and 63- a reduced speed, and means dependent upon a predetermined low temperature of the air in the enclosure for supplying to the air in the enclo sure heat generated by said resistor.

3. Apparatus for conditioning the air within an enclosure including'a refrigerating machine comprising a,compressor and a condenser and an evaporator, an electric motor for driving said air to be discharged into said enclosure, and

means dependent upon a predetermined low temperature of the air in the enclosure for supplying to the enclosure heat generated in said resistor.

4. Apparatus for conditioning the air within an enclosure including a refrigerating machine comprising a compressor and a condenser and an evaporator, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means dependent upon a predetermined condition of the air in the enclosure for utilizing said evaporator to cool and dehumidify air to be discharged into said enclosure, means dependentupon the load requirements of said machine for actuating said control apparatus selectively to determine the operating speed of said motor, and means dependent upon a predetermined low temperature of the air in the enclosure for supplying to the enclosure heat generated in said resistor.

5. Apparatus for conditioning the air within an enclosure including a refrigerating machine comprising a compressor and a condenser and an evaporator; an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means dependent upon the relative humidity of the air in the enclosure for utilizing said evaporator to cool and dehumidify air to be discharged into said enclosure, means including a thermostat responsive to the temperature of the outdoor air for actuating said control apparatus selectively to determine the operating speed of said motor.

said last mentioned means being arranged to decrease the speed of said motor upon a lowering of the temperature of the outdoor air below a predetermined value, and means dependent upon a predetermined low temperature of the air in the enclosure for supplying to the enclosure heat generated in said resistor.

6. Apparatus for conditioning the air within an enclosure including a refrigerating machine comprising a compressor and a condenser and an evaporator for cooling the air in-the enclosure, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means for circulating air over said resistor to remove heat generated thereby. and means operable in a first position to utioutside the enclosure the air circulated over said resistor.

7. Apparatus including a duct for conditioning the air within an enclosure, means for circulating air through said duct and into the enclosure, means including a refrigerating machine having a compressor for cooling air circulated through said duct, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced 'speed of said motor, means including a duct for-circulating air over said resistor and operable ina first position to discharge the air externally of the enclosure and in a second position to discharge the air into the enclosure, and means dependent upon a predetermined condition of the air within said enclosure for actuating said control apparatus to operate said motor at a reduced speed and to actuate said last mentioned means to its second position to utilize heat generated in said resistor for reheating air cooled by said refrigerating machine.

8. Apparatus including a duct for conditioning the air within an enclosure, means for circulatingair through said duct, and into the enclosure,

means including a refrigerating machine having a compressor for cooling air circulated through said duct, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means including-a duct for circulating air over said resistor,

means selectively operable to a-first position for means to its first position to circulate air over said resistor and into said enclosure.

9. Apparatus including a duct for conditioning theair within an enclosure, means for circulating lize air circulated over said resistor for heating 7 the air in the enclosure and operable in a second position for discharging to the atmosphere air through said duct and into the enclosure, means including a refrigerating machine having a compressor for cooling air circulated through said duct, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means including a duct for circulating air over said resistor, selectively operable means movable to a first position for directing air circulated over said resistor into the enclosure to heat the air in the enclosure and movable to a second position for directing air circulated over said resistor to the atmosphere outside the enclosure, means responsive to the temperature of the air in the enclosure for effecting operation of said refrigerating machine, means dependent upon the relative humidity of the air in the enclosure for eflecting operation of said refrigerating machine, means dependent upon a predetermined minimum permissible temperature of the air in the enclosure for maintaining said selectively operable means in its first position, and means dependent upon a condition of the outdoor air for actuating said control apparatus to determine the speed of said motor when operation of said refrigerating machine is effected by said relative humidity dependent means.

10. Apparatus including a duct for conditioning the air within an enclosure, means for circulating airthrough said duct and into the enclosure, means including a refrigerating machine having a compressor for cooling air circulated through said duct, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of saidmotor, means including a duct for circulating air over said resistor, means selectively operable to a first position for directing air circulated over said resistor into the enclosure and operable toa second position for directing air circulated over said resistor to the atmosphere outside the 1 means dependent upon a reduced load require- 1 enclosure, means responsive to the temperature of the air in the enclosure'for effecting operation of said refrigerating machine and for actuating said control apparatus to determine the speed of said motor, humidity responsive means dependent upon the relative humidity of the air in the enclosure for effecting operation ofsaid refrigerating machine when said temperature responsive means is satisfied, means dependent upon the temperature of the ourtdoor air for actuating said control apparatus to determine the speed of said motor when operation of said refrigerating machine is efieoted by said humidity dependent means, and means dependent upon a predeter mined low temperature of the air in the enclosure for actuating said selectively operable means to its first position to circulate air over said resistor and into said enclosure.

11. Apparatus including a duct for conditioning the air within an enclosure, means for circulating air through said duct and into the enclosure, means including a refrigerating machine having a compressor for cooling air circulated through said duct, an electric motor for driving said compressor, control apparatusfor said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, means including a duct for circulating air over said resistor, means selectively operable to a first position for directing air circulated over said resistor into the enclosure and operable 'to a second position for directing air circulated over said resistor to the atmosphere outside the enclosure, and means dependent upon a predetermined condition of the air in the enclosure for effecting operation of said refrigerating machine and for actuating said selectively operable means to its first position to circulate air over said resistor and into said enclosure.

-12. An air conditioning system including a cooling unit for cooling the air within an enclosure, a refrigerating machine including a com-1 pressor for supplying refrigerant to said cooling unit, a prime mover for driving said compressor,

control means arranged to vary the speed of said pressor for supplying refrigerant to said cooling unit, an electric motor for drivingsaid compressor, means including a resistor in a circuit ofsaid motor for operating said motor at a reduced speed whereby heat is generated in said resistor,

ment of said machine for actuating said last mentioned means to reduce the speedof said motor, and means dependent upon a condition of the air in the enclosure for supplying heat .generated in said resistor to the air in the enclosure. v

14. An air conditioning system including a cooling unit for cooling the air within an enclosure, 9. refrigerating machine including a compressor for supplying refrigerant to said cooling unit, an electric motor for driving said compressor, control means including a resistor for operating said motor at a reduced speed whereby heat isigenerated in said resistor, means dependent upon the relative humidity of-the air in the enclosure for energizing said motor to operate said refrlgerat-' ing machine, means dependent upon the temperature of the atmosphere outside said enclosure for actuating said control means to determine the speed of operation of said motor, and means for discharging into said enclosure heat generated in said resistor at reduced speeds of said motor. 15. Apparatus including a duct for conditioning the air within an enclosure, means for circulating air through said duct and into the enclosure, means including a refrigerating machine having a compressor for cooling air circulated through said duct, an electric motor for driving said compressor, control apparatus for said motor including a resistor for providing a plurality of motor speeds whereby heat is generated in said resistor at a reduced speed of said motor, said resistor being arranged within said duct whereby air circulated through said duct passes over said resistor before being discharged from said duct, and means dependent upon a predetermined condition of the air within said enclosure for actuating said control apparatus to operate said motor at a reduced speed whereby air cooled within said duct is reheated by heat generated within said resistor.

16. Apparatus including a duct for conditioning the air within an enclosure, means for circulating air through said duct and into the enclosure, means including a refrigerating machine having a compressor for cooling, air circulated through said duct, an electric motor for driving said oompressor, control apparatus for said motor for providing a plurality of motorv speeds, said control apparatus including two resistors, one located outside said duct and the' other located within said duct, means responsive to the temperature of the air in the enclosure for effecting operation of said refrigerating machine and for actuating said control apparatus to utilize said one of said resistors for providing a reduced speed of said motor, means dependent upon the relative humidity of the air in the enclosure for effecting operation of said refrigerating machine when said temper-' ature responsive means is satisfied, and means dependent upon a predetermined low temperature of the air'in the enclosure for actuating said control means to utilize said other of said resistors for operating said motor at a reduced speed and for reheating air circulated through said duct.

ALEXANDER R. STEVENSON, J'Rn I 

